Processes for forming resist patterns on the surfaces of substrates typically comprise forming a photo-sensitive layer on the surface of the substrate, irradiating portions of the photo-sensitive layer with actinic light, and developing the irradiated layer. If the solubilization of the photoresist increases when exposed to actinic light, it is referred to as a “positive-acting” photoresist; the relatively high molecular weight positive-acting photoresist material depolymerizes, or undergoes breakage of the polymer bonds, upon exposure to actinic radiation thereby rendering the treated compound more easily dissolved by developing solution. If the solubilization of the photoresist decreases when exposed to actinic radiation, it is referred to as a “negative-acting” photoresist; the relatively low molecular weight negative-acting material crosslinks upon exposure to actinic radiation and, thus, it is the non-treated compound that dissolves upon exposure to the developing solution.
Photoresists are often used to protect the underlying substrate from the effects of a subsequent etching process. Defects in the resist pattern, such as inadequate coverage over certain parts of the substrate or inadequate development of the irradiated layer, can result in problems in the completed product. Accordingly, it is important to employ a photoresist whose irradiated layer can adequately be developed and that forms a uniform layer over all surfaces of the substrate to be protected
Photoreactive polymers are particularly useful as binder resins in photoresist compositions employed in photodevelopment of electronic components such as circuit boards and other products. Positive-acting resists have certain advantages in the manufacture of circuit boards; defects that will occur in the manufacture of circuit boards are easier to repair when positive-acting resists are used as compared to when negative-acting resists are used. The irradiation of the photoresist, in the case of circuit board manufacture, often occurs through a glass or plastic cover sheet. The use of “masks” or “art work” prevents exposure of desired areas of the photoresist to UV light.